Effect of processing conditions on the corrosion performance of lasersurfacemelted AISI 440C文档格式.docx
- 文档编号:22565776
- 上传时间:2023-02-04
- 格式:DOCX
- 页数:19
- 大小:67.82KB
Effect of processing conditions on the corrosion performance of lasersurfacemelted AISI 440C文档格式.docx
《Effect of processing conditions on the corrosion performance of lasersurfacemelted AISI 440C文档格式.docx》由会员分享,可在线阅读,更多相关《Effect of processing conditions on the corrosion performance of lasersurfacemelted AISI 440C文档格式.docx(19页珍藏版)》请在冰豆网上搜索。
cDepartmentofIndustrialandSystemsEngineering,TheHongKongPolytechnicUniversity,HungHom,Kowloon,HongKong,PRChina
Received26July2002;
accepted27October2002.
;
Availableonline21December2002.
Abstract:
LasersurfacemeltingofAISI440Cmartensiticstainlesssteelwasachievedusinga2.5-kWcontinuouswaveNd:
YAGlaser.Thepittingcorrosionbehaviorof
laser
surface-meltedspecimensprocessedunderdifferentprocessingconditionsin3.5%NaClsolutionat23°
Cwasstudiedbypotentiodynamicpolarizationtechnique.Thecorrosionresistanceofall
surface-meltedspecimenswassignificantlyimproved,asevidencedbyashiftfromactivecorrosiontopassivity,awidepassiverangeandalowpassivecurrentdensity.Thepittingpotentialofthe
surface-meltedspecimensP08-440C-25(
POWER=0.8kW,scanningSPEED=25mm/s)andP12-440C-25(
POWER=1.2kW,scanningSPEED=25mm/s)wasincreasedto260and200mV(SCE),respectively,andwasmuchhigherthanthatoftheconventionallyheat-treatedAISI440C.Thepittingcorrosioncharacteristicsofthe
surface-meltedspecimenswerestronglydependentontheprocessingconditionswhichresultedindifferentmicrostructures.Theenhancedcorrosionresistancewasattributedtothedissolutionorrefinementofcarbideparticlesandthepresenceofretained
austenite.
Theamountofcarbidesinthemeltlayer,whichindirectlydeterminetheCrcontentinsolidsolutionandhence,thecorrosionresistance,wasrelatedtotheamountofCremaininginsolidsolutionandtodecarburization.Thepitmorphologyofthe
surface-meltedspecimenwasalsostudied.
AuthorKeywords:
Lasersurfacemelting;
Pittingcorrosion;
Martensiticstainlesssteel;
Nd:
YAGlaser
1.Introduction
Inmostpracticalapplicationsofengineeringcomponents,materialssufferfromdeteriorationbymechanicaland/orchemicaleffectspresentintheiroperatingenvironments.Martensiticstainlesssteelsarewidelyusedinengineeringapplicationssuchassteamandwatervalves,pumps,turbines,compressorcomponents,shafting,cutlery,surgicaltools,bearingsandplasticsmoulds,etc.whichdemandhighstrengthandhighresistancetowearandcorrosion.Amongthemartensiticstainlesssteels,AISI440Chasgoodmechanicalproperties(Table1),ahighchromiumcontent(17wt.%)andahighcarboncontent(1.1wt.%).However,thecorrosionresistanceofAISI440Cisthelowestamongthestainlessgroupsbecauseofitshighcarboncontent,whichresultsintheprecipitationofcarbidephases,althoughitschromiumcontentisclosetothatofAISI304austeniticstainlesssteel(18wt.%Cr).
Table1.Typicalmechanicalpropertiesofselectedstainlesssteels
Theapplicationof
surfacemodificationtoprolongtheservicelifeofengineeringcomponentsexposedtoaggressiveenvironmentshasgainedincreasingacceptanceinrecentyears.
Laser
surfacemelting(LSM)hasbeenproventobeapromisingmethodforimprovingcorrosion,wearandfatigueresistancesbyrefining,homogenizingortransformingthemicrostructureofawiderangeofengineeringalloys[1].Thesuperficiallayerofthecomponentsismodifiedwhilethebulkpropertiesofthesubstratearepreserved.AgreatdealofworkhasbeendonetoinvestigatetheeffectofLSMontheelectrochemicalcorrosionpropertiesofAISI304[2,3,4and5],316L[4]and310[5]austeniticstainlesssteels,Zeron100(superduplexstainlesssteel,UNSS32760)[4],AISI430ferriticstainlesssteel[5]andAISI420martensiticstainlesssteel[5,6and7]insodiumchloridesolution.Thepittingcorrosionresistanceof
surface-meltedAISI304[2,3and5]and316L[4]wasimprovedbecauseoftheremovalorredistributionofmanganesesulfideinclusions.For
surface-meltedAISI430andZeron100,theircorrosionbehaviorwasstronglydependentonthephasesformed[4and5].For
surface-meltedAISI430,ahighercorrosionresistancewasobtainedwithamicrostructurecontainingasingleferriticorausteniticphase[5].
Formartensiticstainlesssteels,LSMcausesthedissolutionoflargecarbides,refinementofthemicrostructureandhomogenizationofchemicalcomposition[8],resultinginimprovementofhardness,toughness[9],wearresistance[10]andcavitationerosionresistance[6]ofthesesteels.Thecorrosionbehaviorof
surface-meltedAISI420inNaClsolution[5,6and7]andinH2SO4[11]wasreportedbyseveralworkers.Thecorrosionresistanceof
surface-meltedmartensiticstainlesssteelswasfoundtobehighlydependentonthemicrostructuralchangewhichwasrelatedtoprocessingconditionssuchaspowerdensityandscanningspeedofthe
beam[5,6and7].EscuderoandBello[7]reportedthatthebestcorrosionbehaviorof
surface-meltedAISI420wasobservedinthecompletelymeltedregion.Ontheotherhand,itwasreportedthatLSMimprovedthepassiveperformanceofAISI420andthepittingcorrosionresistanceinH2SO4approachedthatofAISI304[11].
Retainedausteniteiscommonlypresentin
surface-meltedmartensiticstainlesssteels[10,12,13and14].ColacoandVilar[13]reportedanincreaseintheproportionofretainedaustenitewithdecreasingpowerdensityandincreasingscanningspeedintheLSMofAISI420martensiticstainlesssteel.Theeffectofthepresenceandamountofretainedausteniteonthecorrosionbehaviorisstillacontroversialissue.Noharmfuleffectofretainedausteniteonthecorrosionresistanceofa13%-CrmartensiticstainlesssteelwasobservedbyKimuraetal.[15].Ontheotherhand,Kraposhin[16]reportedthattherewasanoptimumamountoftheretainedausteniteforbestresistancetoanodicdissolution.
StudiesrelatedtotheeffectofLSMonthecorrosionbehaviorAISI440Cmartensiticstainlesssteelarescarceintheliterature.Thepresentwork,thus,aimsatimprovingthepittingcorrosionresistanceofAISI440Cin3.5%NaClsolutionbyLSM,andatinvestigatingtheeffectofretainedausteniteandundissolvedcarbidespresent.Therelationshipbetweenthecorrosionparametersandthe
processingconditionswillalsobestudied,aimingatfindingtheoptimumprocessingparameters.
2.Experimentaldetails
2.1.Materialandspecimenpreparation
Theas-receivedAISI440C(designatedasAR-440C)wasinannealedconditionandintheformofroundbarwithahardnessof260Hv.Thenominalchemicalcompositioninwt.%was:
17%Cr;
0.75%Mo;
1%Mn;
1.1%C;
1%Si;
0.049%P;
0.03%S;
andbalanceFe.HardenedspecimenofAISI440C(designatedasHT-440C)wasachievedbyconventionalheattreatmentinafurnaceforcomparisonwiththe
surface-meltedspecimens.Thespecimenswerepreheatedto,andkeptat,850°
Cfor45minandthenheat-treatedthroughtheaustenitizingtemperature(1060°
C)for30min,followedbyquenchinginliquidnitrogen.Temperingwasachievedbykeepingthespecimensat250°
Cfor210min,followedbyaircooling.
Thespecimensforpolarizationstudiesweremachinedtodiscs12.7mmindiameterand3.2-mmthick.ThesurfaceofthespecimensforLSMwassandblastedinordertoreducethereflectivitytothe
beam.Priortopolarizationtests,thesurfaceofall
surface-meltedspecimenswasmechanicallypolishedwith1-μmdiamondpasteinordertokeepthesurfaceroughnessconsistent.Thespecimenswerecleaned,degreasedanddriedbeforethepolarizationtest.
2.2.
surfacemelting
LSMwascarriedoutusinga2.5-kWCWNd:
YAG
laser.Thelaser
beamwasfocusedontothespecimenwithaBK-7glasslensoffocallength100mm.Preliminarytrialsonthe
processingparametersforfeasibletreatmentconditionswerecarriedout.
power(P)of1.2kW(4.2kW/cm2)and0.8kW(2.8kW/cm2)atworkpiecewitha
spotsizeof6mmindiameterandbeamscanningspeeds(v)of25to85mm/swereused.Atscanningspeedslowerthan25mm/s,theenergyinputfromtheYAG
wastoohighandthermaldistortionofthespecimenoccurred.Atscanningspeedhigherthan85mm/s,crackswerepresentinthemeltlayerduetoveryhighcoolingrate.Argonflowingat15l/minwasusedasshieldinggas.ThedesignationsofthesamplesareshowninTable2.Themeltsurfacewasachievedbyoverlappingofsuccessivemelttracksat50%trackwidthinterval.
Table2.
parametersfor
surfacemeltingofAISI440C
2.3.Metallographicandmicrostructuralexamination
AfterLSM,thespecimensweresectioned,polishedandetchedinacidicferricchloridesolution(25gFeCl3,25mlHCland100mlH2O).Themicrostructureandpitmorphologyofthe
surface-meltedlayerswerestudiedbyopticalmicroscopy(OM),scanningelectronmicroscopy(SEM)andenergy-dispersiveX-rayanalysis(EDX).ThephasespresentwereidentifiedbyX-raydiffractometry(XRD).TheradiationsourceusedwasCuKαwithnickelfilterandgeneratedat40kVand35mA.
2.4.Electrochemicalmeasurements
Polarizationstudieswereperformedin3.5%NaClsolutiontoinvestigatetheelectrochemicalcorrosionbehavioroftheas-received,theconventionallyheat-treatedandthe
surface-meltedspecimens.Cyclicpoten
- 配套讲稿:
如PPT文件的首页显示word图标,表示该PPT已包含配套word讲稿。双击word图标可打开word文档。
- 特殊限制:
部分文档作品中含有的国旗、国徽等图片,仅作为作品整体效果示例展示,禁止商用。设计者仅对作品中独创性部分享有著作权。
- 关 键 词:
- Effect of processing conditions on the corrosion performance laser surfacemelted AISI 440C 440
链接地址:https://www.bdocx.com/doc/22565776.html